Healthy diets and semen quality

“Der mensch ist was er isst (man is what he eats)” – Ludwig Feuerbach, 1963

If a man is what he eats then so are his sperm, so it follows that a man’s diet should influence his fertility. Unfortunately, “there are no clear dietary guidelines to counsel men in couples trying to become pregnant”¹.

Obesity is an obvious consequence of a poor diet, and is associated with poor semen quality in humans² and experimental animals³. For experimental animals, this negative effect of diet-induced obesity extends to conception rates³. There is no such data for humans.

A recent systematic review and meta-analysis, examining diet and outcomes of couples using assisted reproductive technology (ART), was critical of the “scarcity of research addressing the relation between male dietary patterns and infertility”⁴. A study of male diet and ART outcomes of 245 couples, published around the same time, found that adherence to a healthy diet “is not related to major outcomes of infertility treatment with ART or semen quality”⁵. Of course, men who are accessing ART may have problems with spermatogenesis or other reproductive functions that are simply not responsive to dietary intervention.

Investigations of diet and semen quality in men without a history of fertility problems provide evidence more relevant to most men than studies of selected groups of men using ART. A recent systematic review and meta-analysis of studies examining the effects of diet on semen quality⁶ provides a summary of the available, albeit limited, evidence.

Cao et al. identified six cross-sectional studies that characterised the diets of men and related them to semen parameters. Four of those groups of men were seemingly healthy and two groups had fertility concerns. The studies were based in USA and Europe, and their quality was moderate or high. All used food frequency questionnaires to determine dietary patterns. Overall, healthy dietary patterns were associated with higher sperm counts and concentrations and better progressive motility. Unfortunately, results from healthy and infertile subjects are combined in the meta-analysis but examination of the forest plots suggests that the benefits can be attributed to studies of healthy men.

Like much of the scientific literature on male reproduction, the studies examined by Cao et al. used semen analysis results as proxy measures of male fertility but “associations with semen quality do not imply associations with fertility”⁷. We’re not likely to have a randomised controlled trial investigating the effect of male diet on pregnancy or birth rates, so information from observational studies with retrospective collection of dietary data and indirect measures of fertility may be the best we will have to counsel men.